Generously coat a large heatproof bowl with non-stick cooking spray, place popcorn and pepita seeds in the bowl, and toss to combine; set aside.
Place pumpkin pie spice, brown sugar, honey, water, apple cider vinegar, and salt in a medium saucepan and stir to combine.
Place pan over high heat, stirring until sugar is completely dissolved; about 2 minutes.
Bring mixture to a boil and cook until it registers 250°(F) on a candy thermometer, about 6 to 7 minutes.
Remove from heat, stir in coconut oil and vanilla until, and whisk until completely combined.
Immediately drizzle caramel mixture over the popcorn/pepita seeds and stir quickly with a rubber spatula, scraping the bottom of the bowl, until popcorn is thoroughly coated. Press popcorn into a prepared pan (being sure to really press it down) and place pan in the refrigerator for 10 minutes. Cut bars into squares and serve.
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